The best a spin-on filter can do while keeping both sides of the deal is to filter everything from large particulates down to anything as small as 25 microns.
Coincidentally, the gaps between many moving parts in your engine are between 2 and 22 microns in size, depending on the crankshaft position. This means that if there are contaminants in the oil that are no smaller than 25 microns (if the spin-on is doing its very best work), you've got engine wear taking place as long as the engine is running.
Currently, the OEMs are dealing with this contamination by having us change our oil and filter every 5,000 to 7,500 miles as the oil gets saturated with contaminants to the point where it won't provide the minimum protection our engines need. This remedy is the "good enough" solution provided by the OEMs. However, there is a plus to this equation; they know an engine will only last so long before "Y'all come back and see us again."
An oil bypass filtration system is a separate filtration system that operates independently from the full-flow filter that comes on the truck from the factory. A bypass filtration system constantly filters engine oil at its own pace, so the oil can be filtered thoroughly and evenly. It doesn't need to be bothered with making sure adequate oil flow is taking place to supply the engine with its needs. Its only concern is filtering contaminants. It lets the spin-on filter grab all the big stuff that would be disastrous to your engine while it methodically and scientifically cleans the smaller impurities from the oil that cause day-to-day, grinding engine wear.
The head of the FS-2500 unit is made of billet aluminum with separate ports for inlet (dirty) oil and outlet (clean) oil. All oil is forced through the sealed system, pushing it through the element media.